1. Field of the Invention
The present invention relates to apparatus for accurately positioning a laser beam used during surgery, and more specifically to apparatus which uses a manually manipulated mirror to direct the laser beam to the intended target area on the patient.
2. Discussion of the Prior Art
For over fifteen years, laser energy has been used routinely in major and minor surgical procedures. Various surgical laser applications are found in such areas as plastic surgery, dermatology, ophthalmology, otolaryngology, neurological surgery, obstetrics and gynecology, gastroenterology, urology, and general surgery. These procedures typically require precise positioning of a laser beam on the tissue being operated on.
A surgical laser manipulating system currently in use is the MICROLITE manufactured by Coherent Medical Division in Palo Alto, Calif. A remote laser unit typically delivers a laser beam (or beams) to this micromanipulator through an articulated delivery arm. A set of adjustable optics are located between the articulated arm and the micromanipulator to allow the surgeon to adjust the focus of the beam. The micromanipulator system, focusing optics, and viewing optics may be mounted on a movable arm or stand to allow the surgeon to roughly position this equipment in the proper location relative to the patient.
Once the laser beam enters the micromanipulator unit, the beam is deflected by a mirror through approximately ninety degrees towards the patient's tissue that is to be operated on. The mirror is manipulated by the surgeon through a joy stick which is connected to the mirror by way of a simple linkage. The mirror is mounted in gimbals to allow it to rotate several degrees in any direction from its central position. A bracket attached to the inner frame of the mirror directly connects to a spherical joint located in the joy stick ball. For accurate positioning, the linkage reduces the motion of the joy stick so that a larger amount of movement of the joy stick is required for a smaller amount of movement of the mirror.
Only a small portion in the center of the mirror is highly reflective to visible light. This allows the surgeon to view the operation through the rest of the mirror, looking approximately parallel to the laser beam that is reflected off of the mirror. In a typical arrangement, the viewing optics are located above and to the front of the micromanipulator unit, the joy stick is angled upward from the front side of the unit, and the laser beam enters the back side of the unit through the focusing optics and exits through the bottom to the target area on the patient.
During a surgical procedure, a low-energy, visible laser beam, such as a helium-neon laser, is directed through the articulated delivery arm and focusing optics, reflected off of the mirror, and out the bottom of the micromanipulator unit. The surgeon moves the equipment into place over the patient with the aid of the low-powered beam and positions the beam on the exact spot he desires by looking through the viewing optics and moving the joy stick to manipulate the beam. When the surgeon is ready to operate, a high-powered laser beam, such as an invisible carbon dioxide beam, is activated, often by a foot switch, and the high-energy beam travels down the same optical path as the low-energy beam to the same target point. In some procedures, the joy stick may then be used to further move the target point while the high-energy beam is still activated.
This existing micromanipulator system has some shortcomings. Because of the simplicity of the linkage joining the joy stick to the mirror and because of the angle of the mirror in relation to the laser beam, the ratio of laser beam movement to joy stick movement is significantly smaller in the horizontal (left and right) direction of the joy stick than it is in the vertical (forward and back) direction. In other words, if the surgeon moves the joy stick in a circular motion, the laser beam spot on the patient will move in an elliptical path.
Another disadvantage in the existing system is the obstruction of vision caused by the linkage connecting the mirror to the joy stick. In order to get fairly linear and symmetrical motion in the vertical axis, the linkage must connect to the gimballed mirror bracket near its center. This part of the linkage and bracket cover a central portion of the mirror from top to bottom, thereby blocking some of the surgeon's view.
An additional drawback associated with this system is the occurrence of arm and hand fatigue experienced by the surgeon when operating the joy stick. The size of the housing of the micromanipulator has been made as small as possible so that it does not interfere with the patient when it is being positioned and so that the surgeon can see and reach around it. This leaves the joy stick protruding out from the unit with no way of steadying the hand for more accurate and comfortable laser positioning. To overcome this problem, various forms of hand rests have been used. However, the prior hand rests have had limited adjustability and could not be easily moved away from the front of the micromanipulator.
Also, a small amount of play or backlash can occur in the linkage because of the construction of the spherical joint connecting the joy stick and the mirror.